We are restoring a water mill and have recently got our 2 wheels turning once more. One of them is connected to an existing 3phase 10KVa alternator which although a little old seems to be in good condition. It spins and we achieve around 49.5Hz (- more to come when the river rises).

However the expected phase to neutral of c230v is only between 10 and 12. We have been advised this is because as it has stood still for a number of years it has lost much of its magnetism. We are also told this is an easy fix with a DC source and a couple of pieces of wire.

We appear to have 6 connections (3 phase, 1 neutral and 2 voltage adjusters that are connected to a remote rheostat).

Could someone tell us how to get this back to life?

Links to some photos: !http://moulin2roues.com/projects/alternator/Alternator-brushes.jpeg !http://moulin2roues.com/projects/alternator/Alternator-connection-box.jpeg !http://moulin2roues.com/projects/alternator/Alternator-connections.jpeg !http://moulin2roues.com/projects/alternator/Alternator-nameplate.jpeg

!http://moulin2roues.com/projects/alternator/Alternator-rectifier.jpeg !http://moulin2roues.com/projects/alternator/Alternator-rheostat.jpeg

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    \$\begingroup\$ You have to power the rotor (it will have brushes) to get the output voltage. There are probably no permanent magnets in the rotor so you have to externally excite. You could add permanent magnets to the rotor and make it self exciting, but that's a pain to do. I'd suggest need the schematic first to ensure you understand the excitation path and your regulator action, but probably all you need is a 12V car battery with a series diode to kick it off \$\endgroup\$ – Jack Creasey Nov 3 '18 at 17:15
  • \$\begingroup\$ Put a DC source of the correct polarity and voltage across the rheostat wires. Not enough won't do any good. The wrong polarity won't do any good. Too much will burn up your alternator. Oh -- and without knowing what your alternator is designed for, I have no clue what "just right", "not enough" and "too much" may be. It may be that if these things were common that it's the same as everything else, but that's a domain of expertise that I'm not in -- you need an antique off-grid power generation stack exchange for that. \$\endgroup\$ – TimWescott Nov 3 '18 at 17:21
  • \$\begingroup\$ I added some links to photos that may help you guys! \$\endgroup\$ – Tim Nov 3 '18 at 17:53
  • \$\begingroup\$ picture 1 on the right has what appears to be a bridge rectifier with a resistor across it, my guess is that that's where the voltage for the field winding is made, connecting a DC suppy with positive to the top terminal and negative to the bottom terminal should re-magnetise the rotor. are there any markings on that green resistor - they may give a clue as to the approptiate voltage... by the look of the diodes the current required will be less that 1A. \$\endgroup\$ – Jasen Nov 3 '18 at 21:56
  • \$\begingroup\$ I can confirm the top and bottom of the resistor are connected to the brown and orange wires seen in the connection-box photo. These are then linked to the remote rheostat. !moulin2roues.com/projects/alternator/Alternator-rectifier.jpeg !moulin2roues.com/projects/alternator/… \$\endgroup\$ – Tim Nov 4 '18 at 9:57

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